This invention relates to pipe couplings, more particularly--but not exclusively--for plastics pipes, being of the type having a socket with an inner internal portion for location of an inserted pipe, and an outer internal portion of larger diameter with means for location of a sealing ring acting between the socket and the inserted pipe, and a gripping ring also located in the outer internal portion of the socket and adapted to prevent withdrawal of the inserted pipe from the socket.
It is known for the gripping ring to be a radially compressible ring, with the radial compression effected by co-operating frustoconical surfaces on the ring and inside the socket and/or inside a nut screwing on to the socket and having an inwardly directed flange for urging the gripping ring axially into the socket. The disadvantage of this is that it is not possible to know and difficult to judge how much to tighten the nut to obtain a sufficient grip on the inserted pipe without risk of damage.
It is also known for the gripping ring to be a grab ring having deflectable teeth for effecting an automatic grip on a pipe inserted through it, but in addition to the disadvantages of not knowing whether the grip is adequate, whether it will be maintained, and whether the inserted pipe has been damaged, it is necessary for the grab ring to be disposed farther in the socket than the sealing ring so that the latter can seal on a portion of the surface of the inserted pipe not scarred by the teeth of the grab ring. Furthermore, because the pipe cannot be inserted into the socket without the grip being effected automatically it is not possible to effect a trial of the coupling without then having to dismantle its constituent parts.
One object of the invention is to provide a pipe coupling of the type initially described and which obviates the disadvantages of the known type just described.
Another object is to provide a pipe coupling capable of releasing from a pipe and of being re-used without necessitating replacement of the gripping ring.
A further object is to provide a pipe coupling suitable for scaling to any size of pipe and predetermining a wide range of gripping pressures applied by hand or manually with conventional tools.
Yet another object of the invention is to provide a pipe coupling for plastics pipe and which can be made entirely of non-metallic material.